The tenth IMSC, Beijing, China, 2007 - International Meetings on ...

1, In the middle-pattern of El Niño event(the anomalous warm water appears first in the
western of 120°W) and the east-pattern of El Niño event(the anomalous warm water appears
first in the eastern of 120°W), there is a significantly eastward propagation of the strongest
western wind anomalies over the western equatorial Pacific Ocean. Besides, the positive
(negative) equatorial surface current anomalies are associated with the enhanced (weakened)
western wind anomalies. <strong>The</strong> response of the ocean currents to the zonal wind anomaly has a
high correlation with the intensity and the characteristics of the propagation of the zonal wind
anomaly. In the middle-pattern of El Niño event, the western wind anomalies are relatively
stronger, which is favorable for the eastward movement of the positive equatorial surface
current anomalies over the western Pacific. <strong>The</strong>refore, the intensity of such El Niño event is
relatively stronger.
2, In the middle-pattern of El Niño event, over the western Pacific, the anomalous
down-welling of the equatorial ocean currents caused by the convergence of surface zonal
currents anomalies suppresses the up-rush of the deep cold water, leading to the warm
surface water, which also moves eastward with the eastward propagation of the anomalous
down-welling.
3, In the east-pattern of El Niño event, the anomalous down-welling of the equatorial
ocean currents caused by the convergence of surface zonal currents anomalies over the
western Pacific Ocean does not move eastward, and the formation of warm water is relevant to
the regional (120°W east) anomalous down-welling of the equatorial ocean currents caused by
the convergence of surface zonal currents anomalies, which suppresses the up-rush of the
deep cold water. This is considerably different from the feature in the middle-pattern of El Niño
event.
Detecting annual cycle in the modes of low-frequency circulation variability
Speaker: Radan Huth
Radan Huth
Institute of Atmospheric Physics, Prague, Czech Republic
huth@ufa.cas.cz
Modes of low-frequency variability of atmospheric circulation in the extratropics are
commonly detected by rotated principal component analysis (PCA) of monthly or seasonal
means. PCA is usually performed on monthly or seasonal, not annual basis. However, we
were faced with the task of creating time series of the variability modes that would be
equidistant in time with the time step of one month. In this contribution, we compare two
approaches to this task: the first one consists in performing PCA for each month separately
(monthly PCA), similarly to Barnston and Livezey (1987), whereas in the other, PCA is
conducted for all monthly data together (annual PCA). All the analyses are based on 500 hPa
heights from the NCEP/NCAR reanalysis. <strong>The</strong> disadvantage of monthly PCA is that only two
modes can be traced throughout the whole annual cycle: it is the North Atlantic Oscillation
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